Parallel Projection: In this projection, z coordinate is eliminated and parallel lines from each vertex on the object are extended until they intersect view plane. These points of intersections are the projections of vertices. Then, these projections of these vertices are joined by line segments. Types: Orthographic and oblique projection.
Perspective projection: In this projection lines of projections are not parallel and they converge at a point called as the center of projection. In this projection realistic views are produced but relative proportions are not preserved. Types: One point, Two point and three point projection.